The present invention relates generally to a mechanical pencil, and more particularly to a mechanism mounted therein for advancing a slit collet chuck with the lead gripped therein and for retracting the collect chuck with releasing the grasping force of the collect chuck against the lead and upon the lead being projected or stepped a tiny increment from a pencil tip.
A generally known pencil of the type described has a feed tube with jaws for grasping the lead, or a slit collet chuck having a recess for receiving balls and a chuck actuation cylinder having a tapered surface for engaging with the balls to induce a "wedging" function to releasably grasp the lead within the slit collet. In order to achieve a smooth actuation of the inner mechanism for advancing the lead so that the lead is placed forward to a writing position, the chuck actuation cylinder mounted around the collet chuck is first advanced towards the pencil tip with its grasping force being unchanged by means of the wedging function, and then the collet chuck is further displaced forwardly relative to the position of the chuck actuation cylinder to permit the chuck to open to release the grasping force of the collect chuck against the lead. In the known structure, however, when the collect chuck is retracted to its original closed position the radially outwardly opened collet chuck is likely to be first closed and then retracted longitudinally to the original normal position. Accordingly, there are cases and happenstances in which the projected lead accompanies by the retraction of the collet chuck, and therefore, the tiny increment of the lead is again pulled into the pencil, resulting in loss of the increment of the lead. Further, in the known pencil, there is a disadvantage that the collet chuck is not fully opened or moved radially outwardly so as to completely release the grasping force thereof against the lead, and therefore the lead is not fed fully into the pencil tip, and any one of spare leads housed within the pencil is not fully advanced into the collet chuck and into the pencil tip.